In the production of semiconductor elements and liquid crystal display elements and the like, microfabrication techniques based on lithography techniques are widely used, and in recent years, advances in these lithography techniques have lead to rapid progress in the field of miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, as described above, ultraviolet radiation typified by g-line (436 nm) and i-line (365 nm) radiation has been used, but nowadays KrF excimer lasers (248 nm) are the main light source used in mass production, and ArF excimer lasers (193 nm) are now also starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use F2 excimer lasers (157 nm), extreme ultra violet radiation (EUV), and electron beams (EB) and the like as the light source (radiation source).
The resist materials used in lithography techniques must have favorable sensitivity relative to the exposure light source. Generally, a base resin with a film-forming capability is used in the resist material. Conventionally, g-line and i-line radiation have been the most common exposure light sources, and if these light sources are used, then in the case of positive resists, (non-chemically amplified) positive resist compositions that use an alkali-soluble novolak resin as the base resin and a quinonediazide group-containing compound as a photosensitive component have been widely used.
With recent shortening of the wavelength of the exposure light source and increased demands for ever finer dimensions, improved sensitivity and resolution relative to these new light sources are now required of the resist materials. Accordingly, since the advent of the KrF excimer laser, chemically amplified resist compositions that include a base resin and an acid generator that generates acid upon exposure have become the most common type of resist material. In a chemically amplified resist, for example in the case of a positive resist, the resist composition includes a resin that contains acid-dissociable, dissolution-inhibiting groups and displays increased alkali solubility under the action of acid, and an acid generator, and during resist pattern formation, when an acid is generated from the acid generator by exposure, the exposed portions become alkali-soluble.
Furthermore, as the wavelength of the exposure light source has shortened, the base resin used in the resist material has also changed, and for example in the case where a KrF excimer laser is used as the light source, a polyhydroxystyrene (PHS) based resin in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups is generally used. Furthermore, in the case where an ArF excimer laser is used as the light source, a resin having structural units derived from (meth)acrylic acid within the main chain (namely, an acrylic-based resin) in which the carboxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups is generally used.
On the other hand, one technique that has been attracting considerable attention recently is MEMS. MEMS are highly advanced micro systems in which micromachining techniques that enable three dimensional microfabrication are used to integrate a variety of microstructures (including functional elements such as sensors, electrodes, wiring, and connection terminals such as bumps and leads) on top of a substrate. MEMS are expected to expand into a variety of fields including the telecommunications, automotive, medical and biotechnology fields, as the various sensors and the like for the magnetic heads of magnetic recording media and the like.
The micromachining techniques used in the production of these MEMS typically employ lithography techniques. For example, patent reference 1 discloses a method of producing a microdevice such as a magnetic head using a resist pattern of a specific shape.
As MEMS undergo ever increasing miniaturization, resist materials capable of forming high-resolution resist patterns are being demanded in order to enable the required microfabrication to be conducted.
As described above, these miniaturization techniques typically involve shortening the wavelength of the exposure light source, and recently, there have been growing demands for a resist material that exhibits favorable sensitivity to electron beams and is capable of forming high-resolution patterns, for use as a resist material that can be applied to MEMS production processes using an electron beam.
However, although a conventional chemically amplified positive resist composition that uses, for example, a PHS-based resin in which the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups as the resin component exhibits sensitivity relative to an electron beam, the composition does not offer satisfactory levels of the various resistance properties required for MEMS production.
For example, in MEMS production, in order to form minute metal structures such as wiring and connection terminals, a resist material is used to form a resist pattern, and plating is then conducted within the resist-free portions of the resist pattern, but this means that the resist requires resistance to the plating solution or the like (namely, plating resistance). Furthermore, the resist also requires heat resistance to the heat applied during the ion milling or etching or the like that is conducted during post-production steps.
However, if the type of conventional chemically amplified positive resist composition described above is used, then resist pattern swelling and the like occur during the plating treatment, which can cause problems such as peeling of the plating. Furthermore, if heated at a high temperature such as 130° C., the shape of the resist pattern tends to deteriorate as a result of heat sag (wherein the pattern softens as a result of the heat, and is unable to retain its shape) and the like.
Furthermore, techniques for forming high-resolution patterns are being investigated not only from a materials perspective, but also from a process perspective.
For example, multilayer resist methods, including a three-layer resist method that uses a laminate prepared by laminating an organic film, an intermediate film formed from an inorganic film of silica or the like, and a resist film onto a substrate, and a two-layer resist method that is superior to the three-layer resist method in terms of requiring fewer production steps, have also been proposed (for example, see patent references 2 and 3). Using these multilayer methods enables high levels of resolution to be achieved.
However, multilayer resist methods suffer from various problems including reductions in the yield and the throughput as a result of the increase in the number of process steps, and increased costs.
The problem of throughput is particularly critical for lithography processes that use an electron beam. In such lithography processes, although very high levels of resolution can be achieved, the exposure is usually conducted in a vacuum, either by conducting exposure through a desired mask pattern, or by direct patterning. As a result, a pressure reduction operation and purge operation must be conducted, meaning the process takes considerably longer than a process that uses an excimer laser or the like. Furthermore, particularly in the case of direct patterning using an electron beam, conducting patterning of the entire substrate takes an extremely long period of time.
Accordingly, in recent years, methods that involve conducting exposure with two or more different light sources (hereafter referred to as “mix and match” methods) are attracting considerable attention.
In these methods, formation of the entire pattern using the light source that is required for formation of very fine patterns, such as an electron beam, is replaced with a method in which the very fine patterns are formed with an electron beam, whereas those rough patterns that do not require a very high level of resolution are formed using a different light source such as a KrF excimer laser, with the exposure conducted via a mask pattern in a single step, and by reducing the time required to form the rough patterns, an improvement in the throughput can be achieved.
However, as described above, the composition of resist materials generally differs depending on the nature of the exposure light source being used, and resist materials tend not to exhibit sensitivity to three or more different light sources. For example, the non-chemically amplified resists used for exposure with g-line or i-line radiation exhibit no sensitivity relative to a KrF excimer laser or electron beam, meaning this combination of light sources cannot be used in a mix and match method. Consequently, there are restrictions as to the combinations of light sources that can be used in a mix and match method.
Accordingly, there is considerable demand for a resist material that can be used within mix and match methods using combinations of any of the various light sources. Of the various possibilities, the demands are particularly strong for a resist material that can be used in a mix and match method that employs a combination of an electron beam, which enables formation of very high-resolution patterns, with another light source, and particularly the most widely used g-line and/or i-line radiation sources.
As described above, recent shortening of the wavelength of the exposure light source and increased demands for ever finer dimensions have lead to demands for resist materials that exhibit improved sensitivity and resolution relative to these light sources, and for example, patent reference 4 proposes a chemically amplified positive resist composition for a system LCD that includes an alkali-soluble novolak resin in which a portion of all the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups, and an oxime sulfonate-based acid generator (for example, see patent reference 4). This chemically amplified positive resist composition for a system LCD can be used in an exposure step that uses ultra violet radiation typified by g-line or i-line radiation.
In order to enable formation of even finer patterns, the inventors of the present invention used the positive resist composition described above and conducted tests on pattern formation using an electron beam. However, the resolution was unsatisfactory.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2002-110536
[Patent Reference 2]
Japanese Unexamined Patent Application, First Publication No. Hei 6-202338
[Patent Reference 3]
Japanese Unexamined Patent Application, First Publication No. Hei 8-29987
[Patent Reference 4]
Japanese Unexamined Patent Application, First Publication No. 2004-354609